Hot water preparation

The simplest systems are so-called thermosiphon systems. They make use of the physical properties of water, which has a different specific density at different temperatures. Hot water has a lower specific weight, rises and is collected in a container (collecting tank). When the water cools down or is hot, it flows back down and further into the collector to be heated.

The advantage of thermosiphon systems is that circulation pumps are not absolutely necessary and that the systems are inexpensive. However, the application remains limited to areas with short and not pronounced frost periods, as the domestic water is heated directly without a frost-protected heating medium. This type of system has been used in the Mediterranean region for a long time.

Figure 11: Gravity system (schematic) for hot water production:
1: Tapping point
2: Insulated storage tank
3: Heated water circulating upwards
4: Solar collector
5: Fresh water inflow
(Source: Rainer Bielefeld; http://de.wikipedia.org/w/index.php?title=Datei:Thermosiphon2.png&filetimestamp=20060518173448)

In frost-prone areas, on the other hand, solar thermal systems for heating drinking water consist of collectors, a control system with a circulation pump and a well-insulated heat storage tank with a heat exchanger (heat exchanger).